1. Technical Field
The present invention relates to a drive plate for an automotive vehicle, and more specifically to a drive plate for linking an engine crankshaft with a torque converter of an automatic transmission. Here, the drive plate implies a plate disposed midway in a transmission route from an engine to vehicle wheels in an automotive vehicle.
2. Description of the Related Art
FIGS. 1A, 1B and 1C show an example of a prior art drive plate 1 for an automotive vehicle. The drive plate 1 is composed of a body portion 2 formed by pressing a metal plate and a ring gear 3 fixed integral with the outer circumference of the body portion 2 by welding. Further, the body portion 2 is formed with a central mount portion 4 fixed to a crankshaft 6 and an outer circumferential mount portion fixed to a torque converter 7, as depicted in FIG. 1B. Further, as shown in FIG. 1A, a plurality (e.g., eight) of crankshaft mounting holes 4a are formed in the central mount portion 4 at regular angular intervals along a concentric circle, and a plurality (e.g., four) of torque converter mounting holes 5 are also formed in the outer circumferential mount portion at regular angular intervals along another concentric circle. In addition, the central mount portion 4 and the outer circumferential mount portion are dislocated in an axial direction of the drive plate 1 by deforming an intermediate portion A (See FIG. 1A) between the two by a drawing processing. Further, in FIG. 1A, 2a denotes an innermost hole through which the crank shaft is passed, and 2b denotes additional holes formed to reduce the weight of the drive plate 1.
In assembly of the vehicle drive plate 1, an end portion 6a of the crankshaft 6 (See FIG. 1B) is fixed to the drive plate 1 with a plurality of mount bolts 6b fitted into the crank mount holes 4a; and a boss portion 7a of the torque converter 7 is fixed to the drive plate 1 with a plurality of mount bolts 7b fitted into the converter mount holes 5. After assembly, therefore, it is possible to transmit the torque of the crankshaft 6 to the torque converter 7 and further to absorb a thrust load of the torque converter 7.
In the above-mentioned prior art drive plate 1, however, whenever a thrust load is applied from the torque converter 7 to the drive plate 1, since being formed by a drawing press, the intermediate area A is easily bent. On the other hand, since being formed rigid, the outer area B (See FIG. 1A) is hardly deformed. Consequently, when a thrust load is applied to the drive plate 1, only the intermediate portion A is deformed, and the outer area B is not deformed, as shown by phantom lines shown in FIG. 1C. In other words, since the virtual bending radius (i.e., a deformation distance) L of the drive plate 1 is small, the intermediate area A is deformed at a relatively large deflection angle DA. Under these conditions, although the above-mentioned deformation can absorb the thrust load applied from the torque converter 7 to the drive plate 1, when this deflection angle DA increases beyond a predetermined limit, since a bending stress generated in the vicinity of the central mount portion 6 is concentrated excessively, there exists a problem in that the bending stress exceeds an allowable stress limit, with the result that the central mount portion 4 of the crankshaft 6 is damaged or broken.